1. Field of Invention
The present invention relates to a printer having a mechanism for locking a cover in a closed position and for releasing the mechanism so that when the cover is closed it is held tightly without permitting play in the closed position while also improving operability when releasing the lock and opening the cover.
2. Description of Related Art
In order to enable easily loading and replacing the roll paper in roll paper printers such as used for printing sales receipts, some roll paper printers have a mechanism that opens the paper transportation path from the roll paper compartment to the paper exit when the cover to the roll paper compartment is opened. This type of roll paper printer may have a platen member that opposes the print head, an opposing pressure roller that presses the paper to the paper feed roller, and a stationary knife of a scissor type paper cutter device which includes a stationary knife and a movable knife. The platen member, pressure roller, and stationary knife are disposed to the cover. When the cover opens the platen member, pressure roller, and stationary knife move away from the corresponding opposing members, i.e., the print head, paper feed roller, and movable knife, which causes the paper transportation path to open. As a result, opening the cover, loading the roll paper into the roll paper compartment, pulling the leading end of the roll paper out from the roll paper compartment, and closing the cover results in the paper being automatically threaded through the paper transportation path as is taught in JP-A-2002-308482.
JP-A-2001-158141 teaches a lock mechanism for locking the cover in the closed position using an engagement pin disposed to the printer body and a locking lever having a hook formed on the distal end disposed to the cover for engaging the engagement pin.
The locking lever is urged to the locking side by the force of a spring. When the cover closes, the distal end of the locking lever meets the engagement pin and the engagement pin pushes the locking lever up (or down) as the cover continues to close so that the hook rides over the engagement pin. When the hook rides over the engagement pin the force of the spring moves the hook from the front in the closing direction of the cover (from the back side of the engagement pin) to the locking position where the hook engages the engagement pin, thereby locking the cover closed.
If the hook of the locking lever cannot ride over the engagement pin on the printer body side, this lock mechanism cannot reach the locked position. Extra space is therefore provided behind the engagement pin so that the cover can be pushed beyond the closed position and the hook part of the locking lever can reliably engage the engagement pin.
Because the cover can be pushed beyond the closed position, the cover can move slightly in the opening/closing direction when locked by the lock mechanism. As a result, in some situations, the cover cannot be positioned without having play in the closed position. If the closed position of the cover shifts, the paper pressure roller mounted to the cover may not be able to apply appropriate pressure to the paper feed roller on the printer body side. If the contact position of the rollers shifts, the nipping position of the paper conveyed between the rollers shifts and the paper nipping force of the rollers changes. This causes the paper feed pitch to vary and lowers paper feed precision.
Furthermore, to open the cover a cover opening lever must be operated to move the locking lever in resistance to the force of the spring to the release position, and the cover must be moved in the opening direction while holding the cover opening lever in the lock-release position. More specifically, the cover must be moved in the opening direction to a position where the locking lever will not re-engage the engagement pin when the cover opening lever is released.
Simply operating the cover opening lever thus leaves the locking lever positioned to engage the engagement pin, and if the cover opening lever is released immediately the spring causes the locking lever to return to the locked position engaging the engagement pin and the cover cannot be opened.
The printer of this invention enables the cover to lock in the closed position without play and to reliably open the cover by operating the cover opening lever only once.